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RISS 인기검색어
- 검색키워드
- 저자 : Jianxiong He (검색결과 4 건)
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Differences in Phase Change Processes Upon Heating Between Co and Zn-ZIF-4 Compounds
Kaihui Li,Haiyan Xiao,Jianxiong He,Hong Jiang 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2018 NANO Vol.13 No.3
Zn and Co-ZIF-4 meta-stable compounds adopt the same topology of Zeolitic imidazolate frameworks (ZIF)-4, but differ in the metal nodes (Zn versus Co). Using calorimetric and thermogravimetric analysis, here we characterized their differences in phase change processes. Upon heating, the framework of Co-ZIF-4 meta-stable crystal undergoes the crystal-to-amorphous phase transition at 590 K, which is somewhat lower than the corresponding transition previously reported in the corresponding Zn-ZIF-4. In addition, the recrystallization rate for amorphous Co-ZIF-4 is relatively higher than the corresponding one of Zn-ZIF-4. Finally, the forming Co–zni crystal begins to melt at about 824K, accompanied by quick decomposition, whereas Zn–zni undergoes complete melting which finishes at around 850K without any decomposition. Based on their differences in chemistry for Co and Zn, we elucidated the chemical origin of the discrepancies of phase transition process for Zn and Co-ZIF-4 compounds upon heating.
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A Power-compensated and Dimmable AC Direct LED Driver with High Efficiency
Donglie Gu,Shengpeng Tang,Kexu Sun,Jianxiong Xi,Lenian He 대한전자공학회 2017 Journal of semiconductor technology and science Vol.17 No.6
A dimmable and power-compensated AC direct LED driver for lighting application is presented. A Source-Coupled Pair (SCP) is adopted to realize the soft self-commutating. To maximize the power efficiency, a multi-dimensional optimization method is applied for finding the optimum number of LEDs in each string. Moreover, error analysis for efficiency is introduced to evaluate the impact of circuit mismatches on efficiency. The driver includes a Power Compensation module which enables the LEDs power approximately constant under various AC line voltages. In addition, a low frequency pulse-width modulation (LFPWM) dimming technique is designed to regulate the LED’s brightness. The LED driver IC is designed and implemented in CSMC 700 V 1 um BCD process. The post-layout simulation results show that the system can achieve a high efficiency of 90.2% under typical condition and 220 V|rms, meanwhile realize dimming with a 90% duty cycle, 10 kHz dimming signal. With the proposed compensation scheme, the output power only changes less than 5% under 20% variation in input voltage.
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Shengpeng Tang,Donglie Gu,Xianzhi Meng,Kexu Sun,Jianxiong Xi,Lenian He 대한전자공학회 2017 Journal of semiconductor technology and science Vol.17 No.6
A 3 MHz Si/ 5 MHz GaN-based 48 W boost converter with high speed and high accuracy Peak Current Control Unit (PCCU) is presented. Compared with the conventional Peak Current Mode (PCM) controllers, the boost controller IC adopts a novel PCCU consisting of a fully differential open-loop operational transconductance amplifier (OTA) and a transimpedance amplifier (TIA), which can minimize the feedforward delay and enable the converter to operate at a higher switching frequency. As a result, the dynamic response and peak current accuracy of the converter are improved. In addition, the compensated output of error amplifier in PCCU is moved forward to raise the control accuracy further. This IC is designed in CSMC 0.8 um 60 V BCD process. The post-layout simulation shows that the boost converter with the proposed PCCU can shorten the feedforward delay to 28.01 ns and behave much better than the conventional one in dynamic response as well as peak current accuracy. The proposed converter can operate at 3/5 MHz well with wide duty cycle ranging from 0.167 to 0.750. The maximum line regulation and output regulation is less than 9.6 mV/V and 6.72 mV/V, respectively.
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High alcohol-soluble MoOx gel for interfacial layer in organic solar cells
Jian Xiong,Zhen He,Shiping Zhan,Bingchu Yang,Xiaowen Zhang,Ping Cai,Cong Xu,Xiaogang Xue,Jian Zhang 한국물리학회 2017 Current Applied Physics Vol.17 No.8
Water-free solvent soluble, low-temperature processed metal oxides are important for preparing efficient and stable electronic devices, as well as the convenience in simplifying the device production process. Here we reported a facile approach with the features of low-temperature and solution-based process for the formation of a MoOx (s-MoOx) film as interface layer in polymer solar cells (PSCs). The absorbability, elementary composition, electronic property and surface microstructure of the s-MoOx are investigated in detail by ultravioletevisible spectrophotometer (UVevis), X-ray photoelectron spectrometry (XPS), ultraviolet photo-electron spectrometer (UPS) and atomic force microscopy (AFM). These investigations confirmed that such MoOx xerogel has high solubility in the organic alcohol solvents, such as ethanol and methanol. Meanwhile, this s-MoOx can be applied as the interfacial layer in organic solar cells via a low-temperature treatment (about 100 C) due to its proper physical properties, and a power conversion efficiency (PCE) over 3% was achieved. In addition, the devices with s-MoOx shows excellent air-stability, and the PCE efficiency can maintain about 84% of its initial value after 100 h exposure in air, which is dramatically enhanced comparing with the common devices with PEDOT:PSS layer.
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